Interstellar chemistry

Interstellar chemistry studies how atoms, ions, and molecules form and are destroyed in the gas and dust between stars, where radiation, low temperatures, and sparse collisions shape reactions.

Gas-phase ion–molecule reactions: Reactions between ions and neutral molecules that form or alter molecules in a gas. These fast reactions sustain molecular synthesis even where temperatures are too low for many neutral reactions.
Interstellar medium: The matter and radiation occupying the space between stars in a galaxy. Its gas, dust, radiation, and energetic particles provide the setting for interstellar chemistry.
Astrochemistry: The study of chemical processes in astronomical environments. Interstellar chemistry is a major branch of astrochemistry, alongside chemistry in planetary and stellar settings.
Orion Molecular Cloud: A nearby star-forming molecular cloud in the Orion constellation. Its exposed and shielded regions reveal how irradiation changes molecular abundances.
Gas-grain chemical models: Computational models that couple reactions in interstellar gas with processes on dust grains. Their predictions depend on how accurately they represent poorly constrained surface processes.
Grain-surface chemistry: Chemical reactions on interstellar dust grains, where adsorbed atoms and molecules can meet and react. Dust surfaces enable reactions that are inefficient in the sparse gas, including molecular hydrogen formation.
Molecular cloud: A dense, cold region of interstellar gas and dust rich in molecular hydrogen. Shielding and high density make molecular clouds major sites of complex molecular chemistry.
Radio astronomy: Astronomy that detects radio-frequency radiation from celestial sources. Rotational transitions of interstellar molecules produce radio and millimeter spectral lines.
Taurus Molecular Cloud: A nearby complex of cold, relatively quiescent molecular clouds. Its cold dense cores are laboratories for slow chemistry and molecule freeze-out.
Interstellar complex organic molecules: Carbon-bearing interstellar molecules containing multiple atoms and chemical functional groups. Their formation pathways remain disputed, especially the balance between gas and grain chemistry.

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